It is well known to use surge protection devices to protect electronic circuits from damage during surge events.
The surge current caused by lightning and other power turbulences is a high risk for electronic devices, such as LED drivers and telecommunications devices, which incorporate semiconductor components.
Surge protection devices are used to suppress current surges at the AC input. One common example of a surge protection device is a metal oxide varistor, which has low cost and good performance. When a surge event propagates to the AC power line, the varistor functions to provide a low impedance path to bypass the surge current and clamp the surge voltage.
The lifetime of a metal oxide varistor is however limited and relates to the number of times it has been used to bypass a surge event and the current it has bypassed. When the device has failed, usually it will cause a fuse to break and the AC input is disconnected.
Currently, there are two ways to improve reliability issues caused by the surge protection device. One is to make use of a surge event counter. This provides the number of surge events to the customer. Using this information, the residual lifetime can be estimated. Another way is to use a higher current rating surge protection device.
These solutions are effective but they are costly. They also need additional installation space. For example, a surge counter typically uses a current transformer to pick up the surge signal. This solution is not suitable for small power units such as an LED driver. When selecting a high current rating device, the number of surge events still determines the lifetime of the protection device, and more space is needed for the higher specification component.
US2011/0096445A1 provides a surge current protection circuit. The surge current protection circuit comprises a peak current detector and a current sensing device. The peak current detector detects when a surge current has occurred, by monitoring a change in duty cycle on a node of a HS (high side) switch.